Detecting objects with a proximity sensor sometimes is less than reliable because of inability of light to be received by a proximity sensor receiver under certain conditions. For example, an object placed in very close proximity or in actual contact with a glass interface might not allow light to pass to the receiver side of the proximity sensor. There are two main paths for light to reach the receiver without an object present, either by reflecting below the glass surface or alternatively through the glass itself. This unintended coupling between the transmitter and receiver side is referred to as local coupling; and is detrimental to the operation of the proximity sensor. The local coupling causes some of the transmitted light rays or optical signal to reach the receiver in the absence of an object in front of the proximity sensor. The light rays reflecting below the glass are typically eliminated by placing an isolator barrier between the transmitting and receiving sides of the proximity sensor. The light rays propagating through the glass can be controlled by the thickness of the glass or the extension of the isolating barrier through the glass. That substantially eliminates local coupling, but could create what is known in the industry as a blind spot. A blind spot is a situation where reflected light from an object does not find a path to reach the proximity sensor receiver especially when the object is in very close proximity to the glass or is actually touching the glass. This is made even worse when the object is opaque, for example an object can dark clothing or hair associated with a user. Specifically, dark clothing or hair has low light reflectivity thereby further reduces the possibility of a substantial number of light rays from reaching the receiver side of the optical apparatus. Opaque materials causes light to reflect at the surface or be absorbed by the material. Dark opaque material causes light reflection to be minimal. A human body part such as a face or lips, on the other hand, allows light to pass through and reflects inside the skin surface off of human bones, blood vessels, tissue, etc; thereby causing light to travel a greater distance above the glass to reach the receiver.
As such, the light in the opaque case is forced to reflect much closer to the glass surface when an opaque object is present than would otherwise be the case when light reflects from a greater distance such as the case when a body is in contact with the glass from inside human skin. This opaqueness scenario makes the blind spot problem much worse, especially if the opaque object is dark or has low reflectivity for the transmitted light from the proximity sensor.
Accordingly, there is a need for a method for resolving blind spots associated with proximity sensors.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.